Recently, the mobile computing including access to the Internet during moving of the mobile node has been more and more popular. The mobility is achieved by the fact that the network connection is available even when the mobile node moves. Multimode terminals that can connect to the Internet using a wide range of access technologies such as the third generation (3G) or other cellular networks, General Packet Radio Service (GPRS), IEEE 802.11a/b/g, IEEE 802.16a or Bluetooth® are also becoming popular than before.
Among various portable computers with high networking capabilities such as cellular phones, laptops and PDAs (Personal Digital Assistants), for example, the request for seamless communications with both of wired and wireless networks is increasing. In addition, as the use of multimedia contents increases in video conferences or the like, seamless communications are more considered as the essential and required feature of the mobile connections. In the practical management of the mobility, it is necessary to provide a seamless handoff so that the users do not notice any disruption of communication. The mobile data networks today commonly consist of a plurality of overlapping wireless networks supporting different data rates and geographical areas and can be accessed only via wireless interfaces peculiar to the applicable media.
Every time a mobile node changes the cell, subnet or network, coverage responsibilities need to be switched between the access nodes providing the service. To provide seamless roaming among these networks, it is necessary to make communications among the networks in order to request the reservation of resources for the mobile node. Thus, in case a user in public transportation facilities is accessing the Internet, for example, complicated problems increase as the transfer speed of the mobile node becomes higher. In addition, it becomes more difficult to learn the transfer direction of the mobile node for reservation of the resources with presumption.
On the other hand, learning the position and the intended mobility of the mobile node brings commercial profits in providing services based on the local area along the intended transfer route. For example, a tourist may get some indication about the scenery or attraction as he moves along a street, and the information may be dynamically updated and refreshed as he turns a corner.
Therefore, the recent wireless system faces a problem that the mobile terminal always needs to scan for alternative access network different from the one currently in connection, which requires too much cost for cellular terminals. Still other problems are that special devices and high calculation capabilities are required for dynamic positioning information and that a solution to search for access networks out of the range is lacking.
As a conventional method to solve the above-mentioned problems, it is proposed in the patent document 1 to use a mobile user tracking system and a positioning system. This solution utilizes tracking of the cellular call information history provided by the user terminal. In the patent document 1, however, there is a problem that the positioning system of cellular phones does not have a sufficient accuracy.
As other conventional methods to solve the above-mentioned problems, it is proposed in the patent documents 2 and 5 to use GPS receivers on the terminal or network side in addition to the tracking history in order to improve the forecast accuracy of the user position information. In the patent documents 2 and 5, however, the GPS receiver is indispensable and the forecast based on the history information is correct only when the motion of the terminal is along as any known route such as bus or train route.
As still another conventional method to solve the above-mentioned problems, it is proposed in the patent document 3 that the terminal makes communications with both networks in dual mode and permits access to the service from either network in that process. In the patent document 3, however, there is no description about the terminal position and the fact that it is out of the networks is not informed.
Furthermore, as still another conventional method to solve the above-mentioned problems, it is proposed in the patent document 4 to provide another device that sends virtual wireless base station ID data from a certain position in the wireless system. This may improve the accuracy of mobile terminal position forecast with a modest investment. According to the patent document 4, however, this method works only when several repeaters are in a small area (a building, for example. Still in this case, another device is required on the network side.).
[Patent document 1] [US Patent Application US 20050064844 A1] Derek McAvoy, Oleg Lebedko and Igor Shushakov, “Mobile User Location Tracking System”, US Patent Application 20050064844 A1, 17 Sep. 2004.
[Patent document 2] [US Patent Application US 20050079877 A1] Atsushi Ichimura, “Mobile Object Location Providing Device and Mobile Object Location Providing System”, US Patent Application 20050079877 A1, 19 Aug. 2004.
[Patent document 3] [US Patent Application US 20050083893 A1] Debashish Purkayasth a and Kamel M. Shaheen, “Method and Apparatus for Reporting WLAN Capabilities of a Dual Mode GPRS/WLAN or UMTS/WLAN WTRU”, US Patent Application 20050083893 A1, 31 Dec. 2003.
[Patent document 4] [US Patent Application US 20050113117 A1] Johan Bolin, Rune Johansson and Ari Kangas, “Position Determination of Mobile Stations”, US Patent Application 20050113117 A1, 5 Dec. 2003.
[Patent document 5] [US Patent Application US 20050162314 A1] Patrick G. Bromley, Louis H. M. Jandrell and Michael D. Wise, “Method and System for Processing Positioning Signals Based on Predetermined Message Data Segment”, US Patent Application 20050162314 A1, 17 Mar. 2005.
The problem to be solved by the present invention is explained below, with reference to FIG. 12. FIG. 12 shows the service areas provided by wireless base stations BS1 and BS2 and the service areas provided by access points AP1, AP2 and AP3 as circles. Among BS's and AP's shown in FIG. 12, any pair of BS's or AP's or a set of BS and AP may be on the same link as layer 2 in the OSI reference model or may be on the same network as layer 3.
Mobile node MN has interfaces (IFs) for communications with both of the networks provided by the wireless base stations BS1 and BS2 and the networks provided by the access points AP1, AP2 and AP3. Here, the service areas of the wireless base stations BS1 and BS2 are adjacent to enable seamless communications. The service areas of the access points AP1, AP2 and AP3 are, however, smaller than the service areas of the wireless base stations BS1 and BS2 and some of them are separated (AP1 and AP2/AP3) and some are adjacent (AP2 and AP3).
Suppose, in such a system, the mobile node MN moves from the service area of the wireless base station BS1 to that of the wireless base station BS2 during communications with the networks of the wireless base stations BS1 and BS2 and scans the access points AP1, AP2 and AP3 to search for a network different from those of the wireless base stations BS1 and BS2. This scanning needs to be continued with both interfaces always kept active, which exhausts the battery. On the other hand, even if the provider of the position base service on the network side of the access points AP1, AP2 and AP3 knows that the mobile node MN is approaching and desires to provide services, it cannot provide any service because the mobile node MN is out of the areas of the access points AP2 and AP3 in FIG. 12.